What is an eye and how does it work?

Whenever light shines on something, some light bounces off of it. The eye “sees” by gathering light rays that bounce off objects. The light passes into the eye, which sends a message about the light to the brain. Most animals' brains turn this message into a picture, or image, of whatever the eye is looking at. Insects, birds, fish, mammals, most shelled animals (such as spiders and crabs), and a few kinds of worms see images. Other animals have simple eyes that don't see images. They can only sense brightness or darkness and which direction light comes from.

Most animals that see images have a single lens eye. The parts of a single lens eye are shown above, and they make up the eyeball.

Light rays enter the eye through a small hole in front called the pupil. The pupil looks like a black circle. The colored ring around the pupil is the iris. Muscles in the iris make the pupil bigger or smaller. This controls how much light enters the eye. Light rays pass through the pupil into the lens, which sharpens the light into a point that hits the back wall of the eye, called the retina. The retina is packed with millions of special light-sensing cells called rods and cones.

Rods identify shapes and motion, but they only pick up black and white. Cones identify colors. Rods and cones work together to build an image of what the eye is seeing. This image actually is upside down! The upside-down image travels along the optic nerve to the brain. The brain turns the image right-side-up and identifies what is in it.

Many insects have eyes with lots of lenses, called compound eyes. Their eyes work in a much different way from the single lens eye. Each lens makes a tiny picture, like a piece of a puzzle. As a result, the insect's brain sees a picture that is made up of many pieces.

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Ockham's razor- It's that simple